Since World War II, human innovation has resulted in great strides in automatic navigation of vehicles and other objects. In particular, automatic navigation makes airline flights safer and less expensive, car travel and transportation more versatile and ocean travel more exacting. Furthermore, automatic navigation is heavily employed in missile systems and munitions. Navigation can be automated with both earth-bound devices or orbiting satellites. In its most versatile form, however, automatic navigation is completely self contained and commonly referred to as "inertial navigation."
Early inertial navigation systems used complex mechanical gimbal structures and mechanical devices with spinning wheels. These devices, known as gyroscopes, are capable of defining a fixed direction in space and can determine the change in angle (e.g., the angular rate) of its carrying vehicle with respect to a specified reference frame. For example, if the base of a three-ringed gyroscope is held in the hand with the rotor spinning and turned about in any of the three axes, the rotor axle will continue to point in the original direction in space. This property is known as gyroscopic inertia. If the speed of the rotor decreases, the gyroscopic inertia will gradually disappear, the rotor's axle begins to wobble and will ultimately take up any convenient position.
As early as the 19th century, J. B. L. Foucault mounted a spinning wheel within gimbal rings (a set of rings that permitted the wheel to turn in any direction) and demonstrated that the spinning wheel maintained its original orientation in space regardless of the Earth's rotation. The gimbals allowed the gyroscope to stabilize a mass to which it was attached (e.g., the platform) so that it remained in a fixed attitude relative to a chosen coordinate plane, even as the object moved around any of the three major coordinate axis. Recent inertial navigation systems rely on software and lasers to obtain information from the gyroscope to determine the angular movement of the vehicle to which the gyroscope is attached. Recent technology has also taken one further step by employing orbiting satellites (such as the Global Positioning Satellite system) and newer inertial navigation systems to obtain a higher-precision, higher-accuracy locating device.
Typical gyroscopes include an internal mass or wheel called a rotor wheel capable of spinning rapidly. In suspension, the rotor is typically free to turn in any coordinate axis. When the rotor is spinning, the gyroscope will resist changes in the orientation of its spin axis. This phenomena is explained by the moment of momentum principle which states that a steady spinning mass (possessing angular momentum) resists being disturbed and will produce a reacting torque in response to any disturbance, the disturbance being defined as that which causes the angular momentum vector to experience an angular rate. The reacting torque is then equal to the negative of the vector cross-product of the rate of change of angular position vector (disturbance) and the angular momentum vector of the spinning mass. Thus, as a vehicle (such as a ship or missile) pitches and rolls in various directions, the gyroscope holds the same plane of rotation which is not influenced by the changing directions of the vehicle.
Gyroscopes can be employed mounted to a stabilized platform or base (whose orientation in a moving vehicle remains fixed in space by employing one or more gimbals attached to the gyroscope) to thereby maintain the rotor's orientation regardless of any movement of the base. Gyroscopes can also be mounted directly to a vehicle (known as "strapdown"). Further, gyroscopes can be operated as a "closed loop" or "open loop" system. A closed loop gyroscope system means that a feedback information loop from the gyroscope output introduces a restoring force to the gyroscope, by torquing or platform motions, to maintain the gyroscope at its null (or initial) orientation. An open loop system means that the gyroscope is allowed to operate off its null orientation as it responds to input angular rates.
Gyroscopes are heavily used in guidance, navigation and stabilization applications. For example, gyroscopes can be used to measure the angular deviation of a guided missile from its desired flight trajectory; to determine the heading of a vehicle for steering; to determine the heading of an automobile as it turns; to indicate the heading and orientation of aircraft during and after a series of maneuvers; or to stabilize and point radar dishes and satellites. Gyroscopes respond to vehicle angular rates (e.g., rates of angular change between vehicle axes and reference axes) which allow the computation of the angles between vehicle axes and reference axes. Gyroscopes have also been used in personal computer products such as a computer mouse, for increased control and sensitivity. Furthermore, a gyroscope can counteract the rolling effect on a vehicle, and thus, is a preferred stabilization tool for vehicles such as a ship or missile.
A significant disadvantage of prior art gyroscopes is their size. While early gyroscopes were large units (e.g., more than two feet across) and heavy, gyroscope technology has lead to the development of smaller units, but still in the macroscopic domain. However, as described in the article titled "Surface Micromachined Microengine", E. J. Garcia, J. J. Sniegowski, Sensors and Actuators, A 48, pp. 203-214 (1995), recent advances in surface micromachining have led to the development of electrostatic actuators capable of driving microscopic machinery. Micrometer devices are capable of producing sufficient force and/or torque to drive small objects such as a gyroscope rotor. The present invention discloses and claims a gyroscope which has all of the advantages and uses of a macroscopic gyroscope, but manufactured and used within the microdomain (e.g., mechanical devices which are fabricated on the scale of micrometers, or approximately 1.times.10.sup.-6 meters).
In particular, electrically powered micrometer-sized micro-motors (or "microengines" as they are known) are fabricated to provide rotational motion to an object. The fabrication of these devices involves the etching of a silicon substrate and depositions of thin films of semiconductor materials. The resulting device includes moveable structures such as links and gears. All elements on these devices are fabricated in the microdomain. Such devices are disclosed and claimed in U.S. Pat. No. 5,631,514, titled "Microfabricated Microengine for Use as a Mechanical Drive and Power Source in the Microdomain and Fabrication Process," the disclosure of which is incorporated by reference.
The micrometer-sized invention disclosed herein differs from existing gyroscope devices in several respects. First, until the present invention, gyroscopes with a free-spinning rotor did not exist which were fabricated by micromachinery techniques to achieve functionality in the micrometer domain. Free-spinning rotor gyroscopes can provide up to a thousand times greater sensitivity than a comparably sized vibratory rotor. Second, gyroscopes in the micrometer domain are capable of being mass produced since the process utilizes the same processing which is used to fabricate millions of integrated circuit chips. Further, microdomain fabricated gyroscopes are capable of being electronically integrated with other electronics similarly fabricated on the chip. Another advantage to the present invention is the fabrication of multiple gyroscopes on the same fabrication plane so that each gyroscope is a functional backup device in the event of a major failure of one or more adjacent gyroscopes. Additionally, microdomain fabricated gyroscopes can now be used in applications where cost and size of the device was previously prohibitive.
It is therefore an object of the present invention to provide a gyroscope manufactured and used in the micrometer domain.
It is a further object of the present invention to provide a gyroscope which is driven by a microengine.
It is also an object of the present invention to provide a navigational device sized in the micrometer domain.
It is a further object of the present invention to utilize a microengine to operate and control a microdomain fabricated gyroscope requiring sufficient force or torque to achieve a predefined angular rotation.
It is also an object of the present invention to provide a microdomain gyroscope mechanically and electronically fabricated to achieve high signal-to-noise ratios in position detectors, enhanced-force logic for closed loop sensor devices and digitization of the resulting output data.